The alternator has a "free wheel" function when there is no load, similar to the air con pump, although this has an electo-mechanical clutch. Pressing the air-con button will bring in the compressor and will identify if this is the culprit. Similarly by loading up the alternator with every high load item (air con / rear screen / main & dip) will make that work harder and reveal any problems.
It's all about a process of elimination, removing the aux belt altogether will as been suggested, identify if the problem is with the aux belt or any of its components.
With the engine running take a squint along the line of the aux belt to see if there is any side to side deviation that may indicate a worn bearing. A spray of water on the belt will quieten it briefly if knackered - I wouldn't use WD40 personally.
Brilliant Blue 156 GTA SportWagon | Q2 | KW V1 Coil-overs | Eibach ARB | Wiecher Strut Bar | Wizard Cat-Back
2009 Fiat Panda 100 HP Stealth Edition
Last edited by TOX1C; 26-11-12 at 07:20.